This invention relates to radial carcass pneumatic tires and in particular to automobile tires. More particularly this invention relates to high performance or speed rated tires.
Typically radial carcass tires have a circumferentially extending belt reinforcing structure located between the carcass and the tire tread for reinforcing the crown area of the tire. It is known to have a textile cord reinforced overlay belt located radially outward of the belt structure in order to reinforce the structure against centripetal and/or centrifugal forces encountered during operation. These overlays are generally formed from an elastomeric ply reinforced by cords which extend substantially circumferentially around the tire and are oriented at an angle of about 0.degree. degrees with respect to the equatorial plane of the tire. As used herein the equatorial plane (EP) means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread. The overlay generally forms one or more complete turns around the belt structure.
It is common for the overlay to comprise an annular ply having end portions which overlap to form a splice. The area of overlap can cause a problem with tire uniformity in that it provides an unbalanced portion of the tire. This uniformity problem has increased as the aspect ratios have decreased. The lower aspect ratio tires allow the uniformity caused by the overlap to show through easier. Furthermore during the manufacture of the tire, the overlap splice is subject to loads that can cause a deformation at the splice and may even pull the splice apart.
One prior art attempt to reduce these problems has involved using a straight line splice formed at an angle to the circumferential direction of the tire, e.g. 30.degree.-45.degree.; (See e.g. LU-A-85964). This method, while reducing the distortion of the underlying belts by reducing the slippage at the overlap region of the overlay has not completely eliminated it.
Another attempt has been to give the overlap portion of the overlay a particular shaped configuration, such as a zig-zag (See U.S. Pat. No. 4,325,423). This method still retains localized stress distribution over a relatively small portion of the circumference of the tire and belt distortion cannot be completely avoided.
Other methods or solutions which have been proposed result in costly manufacturing procedures (either time and/or money). For example DE -A-2,824,357 and DE -A-2,82l,093 require a single turn overlay to be preassembled from several smaller sections while U.S. Pat. No. 4,284,117 uses single yarn reinforcing cords which are spirally wrapped around the belts to eliminate the slippage of the overlay.